Electropolishing magnetic articles



Aug, 20, 1957 s. ANZALDI ELECTROPOLISHING MAGNETIC ARTICLES Filed Sept. 29, 1954 D. C JOURCE ALVA 70 .tropolishing solution. tthroughthewire and sleeves, irregularities in the surface .offthei cathode sleeves may be reduced.

United States Patent 2,803,595 ELECTROPOILISHING MAGNETIG ARTICLES Salvatore rAnzaldLfBrighton, Mass., assignor to Raytheon j Manufacturing Company, Waltham, Mass., a corporation of Delaware.

.Applicatiomseptember29, 1954, Serial him-459,027

2 Claims. (Cl. 204-1405) This invention relatesto means for magnetically holdingaplurality of magneticobjects in spaced relation and, more particularly,relates to means for suspending magnetic. cathode sleeves in an electropolishing:solution from .ai'discforming-apertion of a magnetic circuit.

One of the prior methods for electropolishinga group of objects, such .as hollow cathodesleeves, has been to thread a length of tungsten wire through said cathode sleeves and to submerge the string of sleeves in an elec- By passing an electric current In a modification of this method, a short length of tungsten wire bent at the lower end was inserted through each of the sleeves and the upper end of the wire attached to a clip common supporting member; With still Janothert method, =a tabwast affixed.to...one.end.of the cathode sleeve and the tab connected to a common support. These methods, in addition to proving time consuming, have been unpredictable because of the difliculty of obtaining a good electrical contact to each cathode. Also, the cathodes have a tendency to group together, thereby precluding uniform polishing of the entire surface of all the cathodes. Finally, if the supporting wire is immersed in the electropolishing solution, the wire is gradually corroded by repeated contact with the solution and the solution thereby contaminated.

In accordance with the invention, a multiplicity of cathode sleeves to be polished are attracted to the edge of a magnetic disc forming part of a magnetic circuit. The cathode sleeves are oriented about the edge of the disc along the lines of flux of the magnetic field and are arranged in spaced relations more or less radially about the disc. One terminal of a unidirectional source of electrical energy may be connected to the disc by a clip, and the other terminal of said source connected to an electrode immersed in the electropolishing bath. Because of the spacing between adjacent cathodes proper contact between the electrolytic solution and the entire surface of each cathode is achieved and, consequently, uniform polishing of each cathode is assured.

By means of the subject invention cathodes of assorted shapes and sizes may be electropolished simultaneously. The only requirements are that the cathodes be made of a magnetic material and be of a size of the order of magnitude of the disc. If the mganetic disc is made of the same material as the cathode sleeves, the possibility of contamination of the solution and the cathode sleeves with iron from the magnet is eliminated.

Since the permeability of the electrolytic solution is greater than that of air, the tendency toward separation of the immersed objects is enhanced. By making the container of a magnetic material lined with a substance impervious to the corrosive effects of the electropolishing solution, the above effect is even more pronounced.

Referring to the drawings:

Fig. 1 is a view showing the magnet assembly and a 2. pile: of objects. prior to attachmentpof said. objects toxsaid magnet assembly;

Fig. 2 isa view showing the magnet assembly of-Fig. 1 with? the objects aifixed thereto;

Fig. 3 is a view=showing the magnet1assembly, includ.- ing attached objects, ofFig. 2 immersed. in an electropolishingsolution; and I Fig. 4 is a view showingthe deviceofFig. 3 omitting electrical connections and indicating the approximate magnetic field distribution.

As shown in Fig. 1, a group=of magnetic cathode sleeves 10. to be polished, and preferably made of nickel, is placed on a. relatively smooth surface 11' which may be a plate of glass. These sleeves, after polishing, arelater coated with an electroneemissive material toform cathodes for electron discharge devices. A nickel disc 12, that. is, amagneticdiscmade of the same materialas the cathode sleeves, is magnetically attached mom of the pole pieces 14 of'a magnet 15. This magnet as shownisa conventional U-shaped magnet, but any type of magnet, such as a bar magnet, could be used. The jmagnetassembly, including magnet 15 and disc 12, is moved toward the pileof cathode sleeves until the sleeveslare attracted magneticallyto thedisc, as shown in Fig. 2.

As shown in Fig. 4, the magnetic linesof fcrceemanating from pole14 of magnet 15 and traversing disc 12 are shown by broken lines. These magnetic lines of force diverge along substantially curved paths as they recede from pole piece 14 andemerge from disc l2tmore or less radially. The cathode sleeves ltlbecome aligned with themagnetic lines of force, that is, radially with respect'to the disc, in accordance with well-known principles of magnetism. Since magnetic lines of force never cross, cathode sleeves 10 are spaced from one another about the periphery of the disc, as shown in Figs. 2-4.

The portion of disc 12 to which cathode sleeves 10 are attached is immersed in an electropolishing solution 18 contained within a container or tank 17. Solution 18 may, for example, consist of an aqueous solution of sulphuric acid whose specific gravity is approximately 1.5, corresponding to 62% sulphuric acid by weight and 48% of water by weight. Container 17 may be made of a material such as rubber ceramic, lead, or glass, which is impervious to the corrosive effects of the acid solution 18, or may be made of a magnetic material such as iron or steel lined with an acid-impervious material. If a tank made of magnetic material is used it will itself become a portion of the magnetic circuit and the lines of flux will tend to spread outward towards the sides of the tank and thereby help keep the cathode sleeves spread apart.

The positive terminal of a unidirectional source of current 20 is attached to nickel disc 12 as by clip 21 while the negative terminal of said source is attached to a negative electrode 22 positioned partly within solution 18. A current of predetermined magnitude is passed through the electrical circuit, including disc 12, sleeves 10, and solution 18 for a period of time necessary to accomplish a desired removal of material from the cathode sleeves, in accordance with well-known electropolishing techniques.

The longer the metal disc is exposed to the solution the smoother it becomes and the better the contact between the disc and the cathode sleeves. The amount of wear of the nickel disc, however, is relatively small.

If disc 12 is made of the same material as the cathode sleeves, the characteristics are the same and contamination of the solution is prevented. Even in the event that nickel should be deposited on the nickel cathode sleeves, there would be no harm done as in the case of a deposition of iron thereon. Furthermore, the amount of wear of the nickel disc is relatively small as compared with that of iron. Disc 12 preferably should be thick enough only to permit adequate contact between one row of cathode sleeves and the disc. If the disc is made too thick certain ones of the cathode sleeves will tend to align themselves behind others. The alignment of cathode sleeves in more than one plane will adversely affect the current density and tend to prevent consistent removal of material from all the sleeves. If disc 12 is too thick there is also a tendency for some of the sleeves to take up a position with their longitudinal axes more or less parallel to the disc axis, rather than normal thereto, which also prevents uniform polishing of the sleeves. In one embodiment of the invention a disc of the orderof thickness of 71 was used; the size, however, will depend upon the specific application.

As shown in Fig. 4, magnet 15 may be an electromagnet having a coil 23'adapted to be energized by an appropriate energy source. Magnet 15 may be supported with the aid of a nonmagnetic bar 24 arranged transversely of tank 17. 'Any other means for maintaining magnet 15 in a fixed position may, of course, be used. The approximate magnetic field distribution in the'magnetic path including one pole 14 of magnet 15, disc 12, cathode sleeves '10, the gapKincluding solution 18) betweensleeves 10 and the opposite pole 14' of magnet .15 is shown in Fig. 4. For the sake of clarity, only a portion of the entire field is shown; for example, that portion of the flux ex isting in the air gap directly between poles 14 and 14' is omitted. .Magnet 15 must be sufficiently strong to maintain each of the objects 10 fixedly attached to disc 12. This strength may be predetermined, in the case of a permanent magnet, or may be adjusted as desired if an electromagnet such as shown in Fig. 4 is used.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. For example, any object having magnetic properties may be supported. in addition. to cathode sleeves and the invention is not limited to the use of nickel for the disc and objects to be supported. It is accordingly desired that the appended claims be given a broad in-. terpretation commensurate with the scope of the invention within the art What is claimed is:

l. A method of securing articles having magnetic properties in an aqueous electrolytic bath including the steps of magnetically securing an arcuate disc to one .end only of a magnet, magnetically attracting a plurality of said articles into fixed contact with spaced portions of the periphery of said disc, suspending the article-bearing portion of said disc within said bath substantially vertically, and electrochemically removing material from said articles. I

2. A method of electropolishing articles having magnetic properties including the steps of magneticallysecuring an arcuate disc to one pole only of a magnet, magnetically attracting a plurality of said articles into'contact with spaced portions of the periphery of said disc, immersing said disc substantially vertically in an 'electrolytic liquid medium, and passing a current through'said disc and said articles.

References Cited in the filejof this patent UNITED STATES PATENTS Buch Jan. 18, 1916 Australia Apr. 27, .1936 

2. A METHOD OF ELECTROPOLISHING ARTICLES HAVING MAGNETIC PROPERTIES INCLUDING THE STEPS OF MAGNETICALLY SECURING AN ARCUATE DISC TO ONE POLE ONLY OF A MAGNET, MAGNETICALLY ATTRACTING A PLURALITY OF SAID ARTICLES INTO CONTACT WITH SPACED PORTIONS OF THE PERIPHERY OF SAID DISC, IMMERSING SAID DISC SUBSTANTIALLY VERTICALLY IN AN ELECTROLYTIC LIQUID MEDIUM, AND PASSING A CURRENT THROUGH SAID DISC AND SAID ARTICLES. 